The present invention relates to a motor vehicle equipped with a system for controlling the camber of the wheels of the vehicle on a bend.
Motor vehicles are generally fitted with a spring suspension system minimizing the transmission of jolts and allowing for comfortable driving conditions. Parasitic wheel movements are caused, as the suspension travels, depending on the quality of the suspension. The position of the wheels with respect to the body and with respect to the ground can vary, according to the vehicle and according to the vehicle running conditions. In order to determine the position of the wheels of a vehicle, there have been defined the lock, which is the angle formed by the steered wheels with respect to the longitudinal axis of the vehicle when the steering wheel is turned, the toe-in (or toe-out), which is the angle of lock of the wheels in opposition directions from one another when the steering wheel is pointing in a straight line, and the camber, which is the inclination of the wheels with respect to the ground. The wheels of the vehicle are generally also allowed a certain degree of longitudinal travel in order not to detract from the comfort if the wheels slam into a pot hole, for example.
When a vehicle enters a bend, the body tends to lean toward the outside of the bend under the effect of centrifugal force, because of the presence of the suspension, and this causes body roll. At the same time, most of the weight of the vehicle is transferred onto the wheels of the vehicle on the outside of the bend. If the plane of the wheel is not correctly maintained, this additional load on the wheels on the outside of the bend will have a highly unfavorable loading effect on the tire, because the tire will then be in contact with the ground only by an outboard and reduced peripheral portion of the tread strip of the pneumatic tire and this will furthermore lead to premature tire wear.
Specifically, the wheels often incline toward the outside of the bend in a motor vehicle, unlike the situation with motorcycles in which the wheels are always inclined toward the inside of the bend. U.S. Pat. No. 4,159,128 has already proposed a vehicle suspension system equipped with a system for controlling the camber of the wheels of the vehicle on a bend and comprising, for each wheel of the vehicle front suspension, a pair of superposed suspension upper and lower arms articulated at their outboard end to a wheel support, the suspension lower arm being articulated at its inboard end to the vehicle body, while the upper arm is articulated to the upper end of a control lever, this control lever being articulated at its center to the body, and connected at its lower end to a means for controlling a steering rod for the front wheel of the vehicle. In this system, when the vehicle driver turns the steering wheel to cause the wheels to turn toward the inside of the bend, the means for controlling the steering rod causes the control lever to pivot so as to incline the wheel toward the inside of the bend.
However, in a system such as this, the inclination of the wheels can be applied only to steered wheels, and depends only on the wheel lock. It is therefore not able to take account of the centrifugal force or of the speed or of the acceleration of the vehicle.
French Patent Application Publication No. 2 745 757 proposes an assembly forming a suspended axle, comprising a pair of superposed suspension arms articulated, on the one hand, to the wheel support and, on the other hand, to the vehicle body, a damper articulated, on the one hand, to the suspension lower arm and, on the other hand, to a control lever articulated in turn on the body, the pivoting of the control lever being controlled by an actuator in order selectively to incline the vehicle wheels and body with respect to the ground.
In a more conventional and simpler way, to avoid the outboard wheels inclining toward the outside of the bend, certain vehicles have been fitted with negative camber, that is to say with wheels which are preinclined toward the inside of the vehicle, when driving in a straight line, so that on bends, the wheels on the outside of the bend at worst adopt a vertical position with respect to the ground. However, an arrangement such as this leads to excessive fatigue in the tires which, in a straight line, run on the inside of the tread strip.
The aim of the invention is to eliminate the aforementioned drawbacks and to propose a motor vehicle fitted with a system for controlling the camber of the wheels of the vehicle on a bend, which makes it possible to cause at least a slight inclination of the wheels of the vehicle toward the inside of the bend, in order to keep a good area of contact between the tires and the ground, without in any way influencing the body roll and without necessarily being slaved to the lock of the wheels of the vehicle.
To this end, the subject of the invention is a motor vehicle fitted with a system for controlling the camber of the wheels of the vehicle on a bend, comprising, for each wheel of at least one front axle and/or rear axle of the vehicle, a suspension means consisting of a pair of suspension upper and lower arms, articulated at their outboard end to a hub carrier and attached at their inboard end to the body of the vehicle, characterized in that the suspension lower and upper arms of each pair are articulated by their respective inboard end to one and the same pivot transfer lever which is, in turn, mounted on the body by an articulation, the axis of rotation of which is contained in a longitudinal and vertical plane of the vehicle, said pivot lever being capable of pivoting in such a way as to incline the wheels on the appropriate side.
Advantageously, for each pair of suspension arms, the inboard end of the suspension upper arm is articulated approximately at the upper free end of the pivot transfer lever, the inboard end of the suspension lower arm is articulated at an intermediate point on the pivot transfer lever, between its lower and upper ends, the said pivot lever being articulated to the body of the vehicle approximately at its lower end.
In a first embodiment, the two pairs of suspension arms associated respectively with the two transversely opposed wheels of one and the same, front or rear, suspension of the vehicle, are articulated to one and the same central pivot transfer lever. Of course, in this case, the suspension arms have to be long enough to reach a central, longitudinal, vertical plane of the vehicle.
In another preferred embodiment, the two pairs of suspension arms associated respectively with the two transversely opposed wheels of one and the same, front or rear, suspension of the vehicle, are articulated to two separate pivot transfer levers, said pivot levers being articulated on the body at points spaced apart in the transverse direction of the vehicle, so that the suspension is symmetric with respect to a central, vertical, longitudinal plane of the vehicle. In this case, the said pivot levers may be connected together by a connecting rod to form, with the said pivot levers and the body, an articulated parallelogram.
Advantageously, the ratio between the distance separating the lower end and the intermediate point of the pivot lever and the distance separating the upper and lower ends of the pivot lever, is chosen to be greater than a predetermined value so that the centrifugal force applied to the body of the vehicle will automatically, by reaction, cause the pivot lever to incline on the inside of the bend.
It is possible to envisage that, in the case of a front suspension, the suspension arms are connected at their outboard end to the hub carrier by a ball joint connection, a steering rod being connected to the hub carrier, and a damper connecting the body to the said suspension upper arm.
It is also possible to envisage that, in the case of a rear suspension, the suspension lower arm is connected to the hub carrier by a connection with just one axis of articulation parallel to the longitudinal direction of the vehicle, and a damper connects the suspension upper arm to the body.
Advantageously, the pivot lever is articulated with respect to the body of the vehicle in such a way that rotation of the pivot lever with respect to the body is about an instantaneous axis of pivoting separate from mechanical articulation points.
The instantaneous axis of pivoting of the pivot lever may be designed to be horizontal or alternatively inclined in order to induce a steering effect.
The instantaneous axis of pivoting of the pivot, lever may be designed to be above or below ground level, and preferably below the level of the mechanical articulation points.
In a first alternative form, the aforementioned control system comprises an elastic link with limited torsional deformation, connecting the pivot lever to the body at its aforementioned articulation, so that the said elastic link returns the pivot lever to an approximately vertical and longitudinal plane of the vehicle when the vehicle is running in a straight line, and limits the inclination of the said pivot lever with respect to the said plane, on a bend, the inclination of the pivot lever on a bend being brought about by reaction to the centrifugal force applied to the vehicle body.
In another alternative form, the aforementioned control system comprises an actuator carried by the body of the vehicle and connected to the pivot lever, the said actuator being capable of influencing the angular position of the pivot lever in a bend, it being possible for the said actuator to be slaved to the lock of the wheels, to the centrifugal force applied to the body, to the speed of the vehicle and/or to its acceleration.
The invention is also aimed at a motor vehicle equipped with a system for controlling the camber of the wheels of the vehicle on a bend, comprising, for each wheel of a front and/or rear suspension of the vehicle, a suspension means articulated, at its outboard end, to a hub carrier and borne on its inboard end by the body of the vehicle, characterized in that each suspension means is articulated to the body with a degree of freedom in rotation about an axis parallel to the longitudinal direction of the vehicle in order to vary the camber of the associated wheel, and the aforementioned control system comprises an elastic return means for urging the wheel in an approximately vertical and longitudinal plane of the vehicle when the vehicle is running in a straight line, and for limiting the inclination of the said wheel with respect to the ground in a bend, the said suspension means being designed in such a way as to cause the wheel to become inclined with respect to the ground on the inside of the bend, under the effect of the centrifugal force applied to the body. Advantageously, the aforementioned suspension means and the aforementioned control system are as defined in the vehicle described above.
In order to allow for a better understanding of the subject matter of the invention, three embodiments thereof, depicted in the appended drawings will now be described by way of purely illustrative and non limiting examples.